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Merge pull request #2546 from Mark-Simulacrum/triage
Add triage for this week
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‎triage/2026/2026-08-23.md‎

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# 2026-08-24 Triage Log
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A busy week, with a continued stream of improvements to the next trait solver
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and next borrow check implementations. Other than those changes, the week was
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pretty quiet for performance.
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Triage done by **@simulacrum**.
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Revision range: [8fa1c96c..9a4ad59a](https://perf.rust-lang.org/?start=8fa1c96cfd489e4c27654c144ae871ce2c4db6c6&end=9a4ad59ae3073b013cd62f53f8349ddc61a012e8&absolute=false&stat=instructions%3Au)
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**Summary**:
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:-----:|:---------------:|:-----:|
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| Regressions ❌ <br /> (primary) | 0.5% | [0.2%, 1.5%] | 120 |
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| Regressions ❌ <br /> (secondary) | 0.5% | [0.1%, 1.7%] | 162 |
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| Improvements ✅ <br /> (primary) | -0.3% | [-0.3%, -0.3%] | 1 |
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| Improvements ✅ <br /> (secondary) | -3.2% | [-11.8%, -0.2%] | 36 |
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| All ❌✅ (primary) | 0.5% | [-0.3%, 1.5%] | 121 |
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2 Regressions, 4 Improvements, 2 Mixed; 2 of them in rollups
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28 artifact comparisons made in total
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#### Regressions
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Rollup of 11 pull requests [#161289](https://github.com/rust-lang/rust/pull/161289) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=444dcce484c66c8d626806a8556be3b4d3ef381a&end=e71c0f1e3395b10a8c331317be1a5c107bdf7b2e&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:----:|:------------:|:-----:|
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| Regressions ❌ <br /> (primary) | 0.5% | [0.3%, 0.6%] | 6 |
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| Regressions ❌ <br /> (secondary) | - | - | 0 |
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| Improvements ✅ <br /> (primary) | - | - | 0 |
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| Improvements ✅ <br /> (secondary) | - | - | 0 |
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| All ❌✅ (primary) | 0.5% | [0.3%, 0.6%] | 6 |
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Root caused to remove scalar size mismatch interpreter error, make it an ICE instead [#161238](https://github.com/rust-lang/rust/pull/161238).
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Investigation in [#161456](https://github.com/rust-lang/rust/pull/161456) has led to recovering most of the regression.
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Rollup of 20 pull requests [#161458](https://github.com/rust-lang/rust/pull/161458) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=b66219142c937562f2ff8e083be2a2b25b20199e&end=a872286d0a1873caec0291ed4304de3170adbe16&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:----:|:------------:|:-----:|
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| Regressions ❌ <br /> (primary) | 1.1% | [1.1%, 1.1%] | 1 |
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| Regressions ❌ <br /> (secondary) | 0.1% | [0.1%, 0.1%] | 1 |
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| Improvements ✅ <br /> (primary) | - | - | 0 |
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| Improvements ✅ <br /> (secondary) | - | - | 0 |
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| All ❌✅ (primary) | 1.1% | [1.1%, 1.1%] | 1 |
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> image-rs change is a codegen scheduling change. externs doc-json we can
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> probably ignore, it's tiny and secondary. But apart from that, all benchmarks
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> are tilted toward regression (241 green vs 444 red). Not sure it's worth
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> investigating further, though.
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from @panstromek, <https://github.com/rust-lang/rust/pull/161458#issuecomment-5379001772>
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I'm aligned with not investigating further given codegen scheduling is usually
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hard to do productive things about, size of the rollup, and relatively low
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impact (at least deemed significant by tooling).
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#### Improvements
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Fix ordering for `default impl` check in the new solver [#161268](https://github.com/rust-lang/rust/pull/161268) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=124c16e0de934595dfcdb0845cb39d2bcb8b970d&end=3009fdd3756436133ed9ea6b165a655c28f6857a&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:-----:|:--------------:|:-----:|
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| Regressions ❌ <br /> (primary) | - | - | 0 |
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| Regressions ❌ <br /> (secondary) | - | - | 0 |
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| Improvements ✅ <br /> (primary) | - | - | 0 |
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| Improvements ✅ <br /> (secondary) | -0.8% | [-1.3%, -0.5%] | 6 |
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| All ❌✅ (primary) | - | - | 0 |
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add a cache to the `WfPredicates` visitor [#161274](https://github.com/rust-lang/rust/pull/161274) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=8536f4de90e5e781c06e584f8a88de860adc798b&end=def3ee9e4f0fe1429574f402bb624439bbd13fc6&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:-----:|:--------------:|:-----:|
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| Regressions ❌ <br /> (primary) | - | - | 0 |
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| Regressions ❌ <br /> (secondary) | - | - | 0 |
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| Improvements ✅ <br /> (primary) | - | - | 0 |
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| Improvements ✅ <br /> (secondary) | -0.5% | [-0.9%, -0.1%] | 10 |
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| All ❌✅ (primary) | - | - | 0 |
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Optimize `DeepRejectCtxt` [#161211](https://github.com/rust-lang/rust/pull/161211) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=78c04b6a348438fb9396b8864cd34f92fb99cd53&end=c54751567b19c4ceb08b0412d83529c2568cba8b&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:-----:|:--------------:|:-----:|
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| Regressions ❌ <br /> (primary) | - | - | 0 |
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| Regressions ❌ <br /> (secondary) | - | - | 0 |
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| Improvements ✅ <br /> (primary) | -0.5% | [-0.8%, -0.2%] | 17 |
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| Improvements ✅ <br /> (secondary) | -0.4% | [-0.9%, -0.2%] | 36 |
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| All ❌✅ (primary) | -0.5% | [-0.8%, -0.2%] | 17 |
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Update LLVM submodule to latest `release/23.x` branch [#161466](https://github.com/rust-lang/rust/pull/161466) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=baf1f7cc4faa79b938148ad52c53e96c0102cbc4&end=be0ea33bba5000ac134e58acde780af83d908e44&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:------:|:----------------:|:-----:|
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| Regressions ❌ <br /> (primary) | - | - | 0 |
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| Regressions ❌ <br /> (secondary) | - | - | 0 |
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| Improvements ✅ <br /> (primary) | - | - | 0 |
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| Improvements ✅ <br /> (secondary) | -10.7% | [-11.7%, -10.2%] | 3 |
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| All ❌✅ (primary) | - | - | 0 |
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#### Mixed
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Enable `-Znext-solver` on nightly by default [#160619](https://github.com/rust-lang/rust/pull/160619) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=16a623ad672a92409b5c04beb303583c6cf72a7e&end=526c36b4c477994b7905ec6a084d6150e49076f5&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:-----:|:--------------:|:-----:|
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| Regressions ❌ <br /> (primary) | 0.6% | [0.2%, 1.5%] | 124 |
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| Regressions ❌ <br /> (secondary) | 0.5% | [0.0%, 1.6%] | 151 |
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| Improvements ✅ <br /> (primary) | - | - | 0 |
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| Improvements ✅ <br /> (secondary) | -2.5% | [-8.1%, -0.3%] | 27 |
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| All ❌✅ (primary) | 0.6% | [0.2%, 1.5%] | 124 |
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Note that the specific regressions here are a point in time snapshot: we
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continue to see a steady flow of improvements land for the next solver's
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performance. These results also don't include accurately trained PGO (we are
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profiling with the next solver *disabled* right now, see
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https://github.com/rust-lang/rustc-perf/pull/2537).
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Skip computing extra liveness info if borrow_set is empty [#161252](https://github.com/rust-lang/rust/pull/161252) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=a872286d0a1873caec0291ed4304de3170adbe16&end=c656540d6467dee1381f0cbd882412d6bd1cd5ae&stat=instructions:u)
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| (instructions:u) | mean | range | count |
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|:----------------------------------:|:-----:|:--------------:|:-----:|
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| Regressions ❌ <br /> (primary) | 0.1% | [0.1%, 0.1%] | 1 |
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| Regressions ❌ <br /> (secondary) | 0.3% | [0.2%, 0.5%] | 27 |
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| Improvements ✅ <br /> (primary) | -0.7% | [-1.5%, -0.1%] | 11 |
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| Improvements ✅ <br /> (secondary) | -0.3% | [-0.9%, -0.0%] | 19 |
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| All ❌✅ (primary) | -0.6% | [-1.5%, 0.1%] | 12 |
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This is an optimization for the new borrow check implementation; wins outweigh
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the small regressions (if they're real).

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